Crosstalk Mk. 4 V2.0
Released in 1990 by Digital Communications Associates, Inc
For DOS

Crosstalk Mk. 4 (Mach 4) is the complete, full version of Crosstalk.
Crosstalk Communicator is a "lite" budget version of the same
product.

Mk. 4 and Communicator are the successors to the long lived
Crosstalk-XVI product.

Mk. 4 features multisession communications capabilities, allowing 
multiple serial ports to be used and controlled simultaneously. It 
includes a powerful programming language called CASL (Crosstalk 
Application Scripting Language) that provides full program and 
communications activity control, and enabled users to create a wide 
variety of custom applications.